iOS: 8Tracks is already a great web service for finding playlists stuffed with new music to enjoy. The service's new iOS app makes it easier to not just find something new to listen to, but to connect with the DJ that created the playlist, stay up to date on new mixes as they're posted, and discover new songs based on your mood.
8Tracks sports over 600,000 playlists, all created by users, that are organised by genre, style, artist and mood. If you're feeling like something chill to help you work, you can search for "chill" or even "work," and hit play. Having a hard day? Browse for "uplifting" to find a playlist that will help you feel better. When you hear a mix you like, hit the heart to like it, then follow the DJ to see other mixes they've curated.
There's something special about listening to a playlist that's been curated by hand with real thought about how the songs flow together. The app is free (there's an Android version too, though it hasn't been updated recently), and there are no ads -- in the app or in between the songs.